Ethereal addresses act as real IMAP/POP3 accounts. You can access sent and received messages using your favorite email client, whatever that happens to be.
The same account acts as a real inbound email address. You can send emails to that address from anywhere and these messages also end up on the account mailbox.
All account registration can be handled by the Nodemailer API. If you have lost authentication details for a previous account, then just create a new one.